The headphones that came with my SPINN has 4 poles instead of the normal three (L+,R+,GND). I only know two applications where there are 4 poles:
1.) Microphone - In headsets that have a microphone the fourth pole transmits its signal (L+,R+,Mic+,GND)
2.) 4-pole amplifiers - The left and right channel have separate ground. This achieves complete channel separation and achieves high output power at low voltages.
(L+,R+,L-,R-)
So I am wondering, since the headphones do not seem to have a microphone built in, does the SPINN have a 4-pole amplifier?

You've got a great question there. I hadn't realized it but in checking today my SPINN headphones do indeed have a 4-pole plug. This plug works fine on my other players, and other headphones work fine on my SPINN. I'm thinking it simply permits unique grounds for each channel. You get left/left ground and right/right ground. This is a typical 3-pole plug:

Iriver has simply seperated the ground segment into two sections. It's possible the SPINN keeps unique ground for each channel all the way back to the amp. A good test would be to see if those two top poles are connected internally in the plug.

In a quick listen test I don't hear any audio placement difference using these headphones or some other 3-pole ones.

I don't think there is any TV-out capability on the SPINN, which is why some players have a 4-pole jack.